Generally, closed-loop power control is performed to maintain a signal-to-noise ratio (SNR) at a target value determined in a system. To perform a closed-loop power control, a receiver generates a power control command by comparing a received power or signal-to-noise ratio with the target value, and transmits the power control command to a transmitter. The transmitter controls the transmit power based on the power control command.
Power control technology of a Satellite Code Division Multiple Access (SAT-CDMA) mobile communication system is suggested as one of satellite transmission standards for an International Mobile Telecommunication-2000 (IMT-2000) system. It includes both of the up-link and down-link closed loop power control and the up-link open loop power control.
In the SAT-CDMA mobile communication system, the round trip delay (RTD) time taken for a power control command generated in a base station to be reflected on the received power of the base station is very long compared to a terrestrial system. When the RTD time is longer than a power control command period in the SAT-CDMA mobile communication system, power error compensation performance and loop stability become deteriorated.
To overcome the above problem caused by the long RTD time, Saints et al. suggest a power control in U.S. Pat. No. 6,075,914, entitled “Method and Apparatus for Adjusting Thresholds and Measurement of Received Signals by Anticipating Power Control Commands Yet to Be Executed.” In the U.S. Pat. No. 6,075,914, Saints teaches the technology that estimates a received power after the RTD time by considering the RTD time taken for the present power control command to be reflected on the received power, and generates a power control command based on the estimated received power after the RTD time. The power control method, however, does not solve the problem that the communication system is deteriorated by the alteration of a channel during the RTD time.